Et-PFOSA-AcOH

What is Et-PFOSA-AcOH?

Et-PFOSA-AcOH, also printed as EtFOSAA or N-EtFOSAA, is a sulfonamide-based PFAS related to PFOS.

Check the first two letters before you read anything else. Et-PFOSA-AcOH is the ethyl version, and its methyl sibling, Me-PFOSA-AcOH, is a different analyte with a different status in clinical guidance. The CDC's NHANES files use the abbreviation Et-PFOSA-AcOH, with the full name 2-(N-ethyl-perfluorooctane sulfonamido) acetic acid, and the data variable is LBXEPAH (SEPAH in the 1999-2000 file). Papers and some lab reports write EtFOSAA or N-EtFOSAA instead. Biomonitoring California lists the CAS number as 2991-50-6. All of these point to the same compound, which is why a search for one spelling can miss a report that uses another. The chemistry matters more than the spelling. Et-PFOSA-AcOH carries the eight-carbon perfluorinated tail that PFOS has, plus a sulfonamide group in place of PFOS's sulfonate. The UK Committee on Toxicity described this C8F17SO2 group in 2006 as the building block of "PFOS-related substances" that have "the potential to degrade subsequently to PFOS." In a 2009 rat study, oral N-ethyl perfluorooctanesulfonamidoethanol (N-EtFOSE) was converted to PFOS, with PFOS the main metabolite and N-EtFOSAA detected on the way. So Et-PFOSA-AcOH is best read as a stepping stone in that chain, not a product anyone set out to sell. The human data fit that picture. A 2013 study of 420 plasma samples from Halle and Münster, Germany, collected between 1982 and 2009, found EtFOSAA in more than 95% of them. Its levels rose and fell with PFOS, and both declined over the study period, which the authors tied to the phase-out of PFOS-based products that began in 2000. The same study noted that among the compounds it measured, only di-SAmPAP, a food-contact paper surfactant, was used in consumer products. EtFOSAA was not. Which products carried this chemistry is documented only at the category level. ATSDR's 2021 toxicological profile lists protectants for paper and cardboard packaging, carpets, leather, and textiles among the major applications of perfluoroalkyls, and the ITRC's 2017 history notes food-contact paper such as pizza boxes and fast food wrappers. Neither source ties Et-PFOSA-AcOH to a named product. A blood result can't say whether the compound came in directly or formed in the body from a parent compound, and nothing on a lab report distinguishes the two. Then there's the guidance gap. The National Academies' 2022 clinical guidance sums seven PFAS in serum or plasma: MeFOSAA, PFHxS, PFOA, PFOS, PFNA, PFDA, and PFUnDA. It says it chose PFAS that are "commonly reported as detected in NHANES." The framework itself, and how clinicians are told to use it, belongs to PFOS (Perfluorooctane Sulfonate). Et-PFOSA-AcOH isn't in the sum. EPA's April 2024 drinking-water rule names six regulated PFAS, and it isn't among them either. A drinking-water limit applies to water systems, not to a number in your blood, and the National Academies bands apply to the sum of its seven. Neither framework assigns Et-PFOSA-AcOH a number. That absence isn't a statement that the compound is harmless or harmful. It means no body has published a guidance figure for it, so a lab report that lists it has nothing standard to compare it against. Commercial panels reflect the same gap: Quest's nine-analyte PFAS panel (document dated November 2023, revised June 2024) lists MeFOSAA but not EtFOSAA, and NMS Labs' panels list Me-FOSAA but not EtFOSAA either.

Typical reference context

No clinical reference interval exists for Et-PFOSA-AcOH. The table shows what published sources do provide: where the compound sits in two frameworks, and how often a national survey found it at or above a lab's detection limit.

These percentages are population detection rates, not health thresholds. Each file used a different detection limit and method, so compare the direction across cycles, not the decimals. The 2019 California figure is higher than any NHANES cycle, which likely reflects, at least in part, a detection limit roughly nine times lower than NHANES's 0.1 ng/mL.

What changed recently

Research specific to this analyte is thin. Most of the 2023-2026 literature folds it into a PFAS mixture or reports it as detected or not detected, and the sources below are what could be verified.

A 2025 analysis of the ECHO consortium (3,043 pregnant women from twelve cohorts, samples collected between 1998 and 2020) found EtFOSAA below the detection limit in more than half of participants. The authors therefore treated it as detected versus not detected, not as a continuous value. In their models, the likelihood of a detectable result differed by race and ethnicity. It was published online December 15, 2025, and appeared in the May 2026 issue of the Journal of Exposure Science & Environmental Epidemiology.

A 2023 review of PFAS time trends in the Danish population found few EtFOSAA measurements to build a trend from. Biomonitoring California lists it as a priority chemical measured across nine projects, and its 2019 CARE-2 results are in the table above.

On the regulatory side, EPA proposed on May 18, 2026 to rescind four of the six 2024 drinking-water standards: PFHxS, PFNA, HFPO-DA, and the mixture index. That proposal doesn't touch Et-PFOSA-AcOH, because the compound was never in the rule.

Tests often checked alongside this

If Et-PFOSA-AcOH appears on a report, it usually sits among other PFAS analytes from the same panel. The closest neighbors are Me-PFOSA-AcOH, which shares the sulfonamide chemistry, and PFOS (Perfluorooctane Sulfonate), the compound this one can lead toward. The other long-chain analytes on a typical panel have their own pages: PFOA (Perfluorooctanoic Acid), PFHxS (Perfluorohexane Sulfonate), PFNA (Perfluorononanoic Acid), PFDA (Perfluorodecanoic Acid), and PFUnDA (Perfluoroundecanoic Acid). Whether a doctor adds other lab work is the doctor's call.

What to track over time

Two details about the report itself are worth keeping. First, write down the exact name each lab printed, the unit (ng/mL), and the lab's detection limit, because a result below that limit is reported differently from lab to lab (PFUnDA (Perfluoroundecanoic Acid) covers how). Second, panels change. NHANES stopped reporting Et-PFOSA-AcOH for people 12 and older after the 2011-2012 cycle, and common commercial panels leave it off, so a later report that doesn't list it usually reflects a different test menu. When results from several labs sit in one searchable history, those differences are visible instead of confusing.

What to ask your doctor

• Was Et-PFOSA-AcOH ordered on purpose, or is it part of this lab's standard menu?
• The lab printed no reference interval for it. Does any guideline you use apply to this analyte, or only to the PFAS in the National Academies sum?
• Is my value below the lab's detection limit, and what is that limit?
• Should this result be read alongside my PFOS and Me-PFOSA-AcOH results on the same report, and why?

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